Lower back pain is one of humanity's most frequent complaints and is a common problem. According to The University of Maryland School of Medicine, about 60 to 80% of the adult U.S. population has lower back pain, and it is the second most common reason people go to the doctor. Lower back problems affect the spine's flexibility, stability, and strength, which can cause pain, discomfort, and stiffness.
Statistics from the American Chiropractic Association (ACA) reveal that at least 31 million Americans experience lower back pain at any given time.
Lower back pain is the leading cause of disability in Americans under 45 years old. Each year, 13 million people go to the doctor for chronic back pain. The condition leaves about 2.4 million Americans chronically disabled and another 2.4 million temporarily disabled.
Our industrialized society has transformed into an information processing society in which more employees are transacting business, while proper sitting posture declines after long periods of time. With the advent of the information processing age, it is becoming increasingly clear that there is a significant mismatch between people and the furniture in their home and working environments, as evident from the increasing numbers of employees suffering from chronic back pain. The most likely explanation is improper sitting posture. Most of us are not aware of the best sitting positions, thereby resulting in back pain, lower back pain, neck pain, arm pain and hand pain.
Lower back pain can be caused between muscles, tendons, and discs that are connected to each other by the spine. The main source of lower back pain includes:                The large nerve roots in the lower back that go to the legs may become irritated;        The smaller nerves that supply the low back may become irritated;        The large paired lower back muscles (erector spinae) may become strained;        The bones, ligaments or joints may become damaged; and        An intervertebral disc may become degenerating.        
Some simple remedies when followed on a daily basis can help us reduce our back pain. Experts from all over the world have formerly been of the opinion that the proper sitting position is the right angle or erect position.
Posture is the position in which we hold our body upright against gravity while standing, sitting or lying down. Good posture involves training our body to stand, walk, sit and lie in positions where the least strain is placed on supporting muscles and ligaments in order to achieve the following:                keep bones and joints in correct alignment so that muscles are used properly;        help decrease the abnormal wearing of joint surfaces that could result in arthritis;        decrease the stress on the ligaments holding the joints of the spine together;        prevent the spine from becoming fixed in abnormal positions;        prevent fatigue because muscles are used more efficiently, allowing the body to use less energy;        prevent strain or overuse problems;        prevent back and lower backache and muscular pain; and        contribute to a good appearance.        
As shown in FIG. 1 for male and FIG. 2 for female, the sitting bones are literally what humans sit on. The anatomical name is referred to as Ischial Tuberosity. At the center of the diagram in FIGS. 1 and 2 is the sacrum, which consists of 5 fused vertebrae of the human pelvis. What resembles elephant ears on either side of the sacrum is the ilium. At the bottom are two round holes which look like a mask with two eye holes. At the most bottom outer surface of the eye holes of the pelvis are the sitting bones (Ischiums). These bony prominences are felt when sitting on a hard surface with good posture. Tipping the pelvis forward and backward or side-to-side, human subjects become aware of these important bony prominences.
FIG. 3 illustrates how the body is held erect. The thick black lines represent the principal muscles involved in standing. The vertical dotted line indicates the center of gravity, which falls behind the axis of rotation of the hip.
The following Table 1 is a list of male and female body segment percentage weight. Data were derived by de Leva from young athletic Russian subjects in 1996. Data for American and other nationalities in various age categories may very well be different. This data should be sufficient for purpose in this application.
TABLE 1Body Segment percentage weightsSegmentMaleFemaleAverageHead & Neck6.946.686.81Trunk43.4642.5843.02Upper Arms5.425.105.26Forearms3.242.763.00Hands1.221.121.17Thighs28.3229.5628.94Shanks8.669.629.14Feet2.742.582.66TOTAL100%100%100%
On a sitting position on a sofa, the weight of a person's head, neck, trunk upper arms, forearms, hands and about ⅓ of thigh's weight are carried on the sitting bones. The ⅓ value for the thigh's weight is an approximation that could be more or less. That is, 6.94+43.46+5.42+3.24+1.22+⅓×28.32=69.72 represent the total body weight of a male that is carried on the sitting bones. For a male weighing 180 lbs., this is calculated to 69.72%×180=126 lbs. This amount of weight is not aligned with a person's center of gravity, thus, creating a good amount of cantilever force. For as long as a person is sitting, the large paired lower back muscles (erector spinae), many fine muscles, tendons and ligaments in the pelvis area are subjected to severe stress and pressure to keep the body upright against gravity and the cantilever force.
Many complex ligaments connecting Pelvis, Coccyx, Sacrum, Socket Joint of hip and Lumbar Vertebrae (L1-L5) are shown in FIG. 4. Pelvic, Coccyx, Sacrum and Lumbar Vertebrae (L1-L5) are shown in FIG. 5.
These bones are closely connected to each other by large and small muscles, tandems, ligaments, veins, and nerve roots. Prolonged sitting results in extended contraction that restricts veins, nerves and supply of oxygen and nutrition to cells in that area. The irritated and damaged muscles, tandems, ligaments, cartilages, veins and nerves are the main source of lower back pain.
Though sitting down for extended periods of time on sofas, chairs, etc. may be far worse than we realize, a person can minimize its impact by sitting properly. Correct sitting posture means having all the bones in our spine properly supported and lined up correctly.
The following principles of physics and engineering are relevant to achieve proper posture:                1) Body's Center of gravity;        2) Moment of force (weight of hanging legs pulling down femur at knee joint).        3) Femoral head moving in Acetabulum (socket of hipbone of the pelvis); and        4) Inclined surface of Cantilever seat for lift.        
The three skeletons shown in FIGS. 5, 6, and 7 show that the human upper body is supported by the Femur (thigh bone), the Femoral neck and the Femoral head. The center of gravity of the human body is nearly aligned with the head of the femurs, not the sitting bones (ischiums). As a result, when a person sits on a sofa, the pelvic girdle is tilted forward putting much stress on the surrounding muscles, ligaments, tendons, veins, cartridges and nerve cords.
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